1. Field of the Invention
Aspects of the present invention relate to an apparatus for a fuel processor of a fuel cell system, and more particularly, to a hydrogen generator included in a fuel processor, and a method of operating the same.
2. Description of the Related Art
A fuel cell is an electricity generation system that transforms chemical energy directly into electrical energy, through a chemical reaction between oxygen and hydrogen contained in a hydrocarbon group material, such as, methanol, ethanol, or natural gas. Fuel cell systems can be largely divided into fuel cell systems that use liquid hydrogen and fuel cell systems that use hydrogen gas. Fuel cell systems that use hydrogen gas include fuel cell stacks and fuel processors. Fuel cell stacks have a structure in which a few to a few tens of unit cells, each composed of a membrane electrode assembly (MEA) and a separator, are stacked together.
FIG. 1 is a block diagram showing a configuration of a conventional fuel cell system.
Referring to FIG. 1, a hydrogen-containing power generation fuel is reformed into hydrogen gas in a fuel processor, and the hydrogen gas is supplied to a fuel cell stack. In the fuel cell stack, electrical energy is generated through an electrochemical reaction between the hydrogen gas and oxygen.
The fuel processor includes a desulfurizer and a hydrogen generator. The hydrogen generator includes a reformer and a shift reactor. The desulfurizer removes sulfur from the power generation fuel to prevent catalysts in the reformer and the shift reactor from being poisoned by sulfur compounds.
Hydrogen gas is generated from hydrocarbons in the reformer, but in addition to the hydrogen gas, carbon dioxide (CO2) and carbon monoxide (CO) are also produced. The CO acts as a poison to the catalysts used on the electrodes of the fuel cell stack. Therefore, the hydrogen gas generated in the reformer is not directly supplied to the fuel cell stack, but is supplied only after the CO is removed in the shift reactor. Conventionally, the hydrogen gas that has passed through the shift reactor has a CO content of 10 ppm, or less.
In order to remove CO, a shift reaction, a methanation reaction, and a PROX reaction, as shown below in Reactions 1 through 3 respectively, occur in the shift reactor.CO+H2O→CO2+H2  [Reaction 1]CO+2H2→CH4+½O2  [Reaction 2]CO+½O2→CO2  [Reaction 3]
In order to reduce the CO content in the hydrogen gas to 10 ppm or less, using the reactions, the shift reactor must be heated to 200 to 250° C. However, in a conventional hydrogen generator, it takes more than one hour to increase the temperature of the shift reactor to 200° C. or more, using an indirect heating method. Waiting one hour or more to use electrical energy generated from a fuel cell can be a serious drawback in using such a fuel cell system. Therefore, there is a need to improve the heating method.
To solve the above problem, a method of heating the shift reactor using an additional electric heater has been disclosed in Japanese Patent Publication No. 2001-354404. However, the large consumption of electrical energy inherent in the taught method, due to the use of an electric heater, reduces the efficiency of the electrical energy generation.